Investigation of Particle Deposition in Laminar and Turbulent Flows

The transport of particles in laminar and turbulent flows has numerous applications in engineering, biological and environmental systems. The deposition of aerosol particles in channels and pipes, as well as in bends and contractions, is important in many applications including dust inhalation and human respiratory systems, chip fabrication, particle size characterization, and sampling of radioactive aerosols. In this research, we are investigating the flow dynamics and particle deposition on a square cylinder placed in a rectangular channel. Both a stationary and an oscillating cylinder are considered. For the two-phase flow simulations, the unsteady gas flow field is computed by solving the incompressible Navier-Stokes equations using a staggered-grid control volume approach and the Marker-and-Cell (MAC) technique. The gas-phase algorithm has been validated using four test problems involving both steady and unsteady flows. The particle dynamics is simulated using the modified BBO equation. Numerical experiments are conducted to evaluate the relative contributions of various terms in the BBO equation. For particle dynamics in unsteady vortical flows, all the secondary terms are found to be negligible compared to the steady state viscous term at particle density ratios greater than twenty.

The two-phase flow model and the detailed flow visualization are employed to characterize particle dispersion and deposition as a function of the Reynolds number, particle Stokes number (St) and density ratio (e). For the fixed cylinder, particle dispersion in the cylinder wake exhibits a typical non-monotonic behavior. Particles with St < 0.1 behave like fluid particles, whereas those with St between 0.1 and 0.5 disperse more than fluid particles, and those with St > 1.0 are essentially unaffected by the flow in the near wake region. In addition, the small-St particles are distributed in the vortex core, while the intermediate-St particles were distributed around the vortex periphery. For e > 20, the particle deposition is essentially characterized by the Stokes number. The amount of deposition increases precipitously as St is increased from zero to unity, then increases slowly for St between 1 to 3, and is essentially independent of St for St > 3.0. For the range of Reynolds numbers investigated, which includes both laminar and transitional regimes, the Reynolds number (Re) has a negligible effect on particle deposition, but a more discernible effect on particle distribution and dispersion.